The present invention relates to a measuring device for measuring the distance between a reference mark and a target object.
Measuring devices for laser distance measuring systems consist of one electro-optical component embodied as a beam source, another electro-optical component embodied as a detector and a beam forming system having transmitter optics and receiver optics. The beam source and the transmitter optics are referred to as a transmission device, and a detector and the receiver optics are referred to a reception device. The beam source emits a laser beam along an optical axis, this beam being directed at the target object by the transmitter optics. A reception beam reflected and/or scattered by the target object is formed by the receiver optics and directed at the detector along an optical axis. Measuring devices are subdivided into paraxial arrangements, in which the optical axes of the transmitting and receiving devices run with a parallel offset, and coaxial arrangements, in which the optical axes of the transmitting and receiving devices are situated one above the other and are separated with the aid of beam splitting optics. In the case of coaxial arrangements, the transmitter optics and the receiver optics are integrated into a shared beam forming optics, forming the laser beam and the reception beam.
European Patent Document No. EP 1 351 070 A1 discloses a known measuring device having a paraxial arrangement of the transmitting and receiving devices. The beam source, the transmitter optics and the receiver optics are mounted on an essentially rigid optics carrier. The detector is mounted on a circuit board, which is connected to the optics carrier by a screw connection in a mechanically rigid manner. The optics carrier comprises three receptacles for mounting the beam source, the transmitter optics, and the receiver optics. The beam source and the receiver optics are inserted into the receptacles in the optics carrier as far as the stop and are optionally secured in the optics carrier with an adhesive bond. The transmitter optics is adjustable along its optical axis in the optics carrier, is adjusted with the beam source activated and is glued to the optics carrier in the adjusted position. With the beam source activated, the detector is shifted by a manipulator in relation to the circuit board in all three directions in space, i.e., in the direction of its optical axis and in the plane perpendicular to the optical axis until the reception beam strikes a predetermined area of the detector. Then the detector is secured on the circuit board in the adjusted position using a soldered joint. Adjustment tolerances are compensated by adjustment gaps with soldered bridges and enlarged contact faces.
In the case of measuring devices having a paraxial arrangement of the transmitting and receiving devices, it is a disadvantage that the transmitter optics and the receiver optics are arranged side by side in space; and the two optics need more space in a plane perpendicular to the optical axes than is the case with a coaxial arrangement. Furthermore, a parallel offset between the optical axes of the transmitting and receiving device, which is known as parallax, results in the fact that at short distances from the target object, imaging of the reception beam on the active area of the detector is shifted with a decrease in the distance from the optical axis of the receiver optics and undergoes a widening of the beam cross section in the detector plane. Because of the parallel offset between the optical axes of the transmitting and receiving devices, it is necessary to use complex multifocal receiver optics or a segmented detector of a relatively great longitudinal extent in measuring devices having a paraxial arrangement of the transmitting and receiving devices. The multifocal receiver optics ensures that, due to a partially greater refractive power of the receiver optics, light from the near range is refracted more than light from the remote range, such that this light reaches the detector at least partially despite the shift in the reception beam. A segmented detector of a great longitudinal extent results in the fact that a shifted reception beam is not even detected.
Measuring devices having a coaxial arrangement of the transmitting and receiving devices have the advantage of being parallax free in comparison with paraxial arrangements. However, the disadvantage is that there is optical crosstalk from the beam source to the detector because the same optical channel is used for the transmission path and the reception path. Optical crosstalk leads to a cyclic distance measurement error, i.e., a measurement error that changes periodically with the distance. To reduce the problems of optical crosstalk and excess light scatter on air particles or aerosols in the near range, German Patent Document No. DE 203 80 221 U1 proposes an integrated optical component which forms the laser beam and the reception beam so that they surround one another but do not overlap to a great extent in the near range. It is a disadvantage that the optical component is embodied as a lens with a large diameter and a large focal distance, which in turn necessitates a detector with a large active area. On the whole, the design according to DE 203 80 221 U1 is not suitable for constructing an inexpensive and compact measuring device for a laser distance measuring system.
It would be desirable to improve a measuring device with regard to the disadvantages mentioned above. The object of the present invention is to provide an inexpensive and compact measuring device for a laser distance measuring system with a high measuring precision, such that the measuring device should be suitable for use in the near range and in the far range.
According to the invention, an optics carrier having a first receptacle for mounting a first of the electro-optical components and having a second receptacle for mounting the beam forming optics is provided, wherein the optics carrier has a monolithic design. Electro-optical components are optical components such as a beam source or a detector, for example, which must be supplied with electricity for operation and which convert electricity into light and/or convert light into electricity.
A monolithic optics carrier is made of one material and is not assembled from multiple individual parts. Monolithic optics carriers have a connecting zone between the first and second joining partners. A monolithic optics carrier has the advantage over a multipart optics carrier that, under the influence of temperature, the optics carrier undergoes uniform changes, and there are no regions in the optics carrier that undergo different changes as a function of temperature because of different properties of the materials. The stability of the measuring device is increased by the monolithic optics carrier. The optical components can be adjusted accurately in relation to one another and the adjusted positions are retained under various ambient conditions. As the optical components are aligned more precisely in relation to one another and as the stability of this alignment is greater, the active area of the detector may be smaller, the dimensions of the receiver optics required for a high measurement performance may also be smaller, and the entire measuring device may be smaller. Due to a small active area of the detector, very little interfering outside light and/or sunlight is detected. However, more interfering outside light and sunlight are detected because of the larger beam angle due to the reduction in the focal distance of the receiver optics. A small active area of the detector compensates at least partially for the effect of a reduced focus of the receiver optics.
The first of the electro-optical components and the beam forming optics are preferably adjustable in the direction of the respective optical axes during the adjustment of the measuring device in its receptacles. The adjustability of the electro-optical components and the beam forming optics in relation to the optics carrier in a direction of adjustment running essentially parallel to the respective assigned optical axis prevents a gap between the circuit board and the second of the electro-optical components, which would have necessitated bridging by a solder bridge. The fact that the formation of a solder bridge is avoided increases the reliability of the mechanical mount of the electro-optical components and improves the high-frequency properties of the measuring device.
In a preferred refinement of the invention, the second form of the electro-optical components is arranged on a circuit board, where the circuit board is connectable to the optics carrier via a connecting device. The second of the electro-optical components is adjustable in a plane essentially perpendicular to the optical axis of the laser beam or the reception beam which is allocated to the second of the electro-optical components and can be secured in the adjusted position. The plane in which the second of the electro-optical components is adjustable runs essentially perpendicular to the assigned optical axis. A minor deviation from the right angle is tolerable as long as the resulting change in distance from the beam forming optics does not exceed an admissible value. For example, a change in the distance from the beam forming optics of approximately 10 μm is the result of an adjustment distance of 500 μm in the plane perpendicular to the reception beam (detector as the second of the electro-optical components) and an angle deviation of 1°. This change in distance results in a displacement of the focal position which is undesirable during adjustment of the measuring device. The angular deviation may be only of the order of magnitude such that the resulting displacement in the focal position during adjustment of the measuring device is still acceptable. The optical and electro-optical components arranged in the optics carrier are adjustable in the direction of the respective assigned optical axes, i.e., the directions of adjustment of the components run essentially parallel to the optical axes. Deviations from parallel which occur, for example, due to manufacturing tolerance in the optics carrier, are admissible.
The second receptacle for mounting the beam forming optics preferably has a first supporting surface, a second supporting surface and a clamping surface, such that the supporting and clamping surfaces are integrated into the optics carrier. A supporting surface is defined as a supporting area which acts through the gravity of the beam forming optics and the clamping surface is defined as a supporting area which acts not through the gravity of the beam forming optics but instead through an additional force. The supporting and clamping surfaces ensure that the beam forming optics are precisely adjustable in making the adjustment and can be secured in the position after being adjusted. Optionally the beam forming optics may additionally be used through an adhesive bond to the optics carrier. The additional adhesive bond ensures that even with very great mechanical stress such as free fall of the measuring device, the adjusted position is preserved.
The optics carrier especially preferably has a spring element which forms the clamping surface for the beam forming optics. The integration of the spring element with the clamping surface in the optics carrier ensures that the second receptacle for the beam forming optics will undergo uniform changes under the influence of temperature and that a uniform introduction of force into the beam forming optics is ensured.
The second receptacle preferably has at least one guide surface which is integrated into the optics carrier. The alignment of the beam forming optics is improved by the additional guide surfaces, and the risk that the beam forming optics will be introduced into the second receptacle of the optics carrier in a tilted position is reduced. The guide surfaces ensure that the beam forming optics will be aligned accurately in the beam path of the laser beam. As the alignment of the optical components relative to one another is more accurate and more stable, the active area of the detectors, the focus of the receiver optics and thus the measuring device may be designed to be smaller.
In a preferred embodiment, the optics carrier has a third receptacle for mounting the beam splitting optics with three supporting areas, such that the supporting areas are integrated into the optics carrier. The beam splitting optics deflecting the laser beam or the reception beam at least partially must be provided in a coaxial arrangement to spatially separate the laser beam and the reception beam from one another. The beam splitting optics is embodied as a polarization beam splitter, for example.
The first and second supporting areas are especially preferably embodied as wedge-shaped grooves, and the third supporting area is embodied as a planar supporting surface, the beam splitting optics being clamped on the supporting surface with the aid of a clamping element. The clamping element is designed as a spring element, for example, and is arranged so that the spring force acts over the planar supporting surface as much as possible. The contact of the beam splitting optics in the two wedge-shaped grooves ensures that the respective contact forces and the supporting counterforces act on the beam splitting optics largely in opposite directions, preventing any curvature of the beam splitting optics. As the alignment of the beam splitting optics is more accurate and stable with respect to the other optical components, the active area of the detector, the focus of the receiver optics and thus the measuring device may be designed to be smaller.
In a preferred alternative embodiment, the beam splitting optics is embodied as a pinhole mirror consisting of an opening and a reflective coating, such that the opening is integrated into the optics carrier and the reflective coating surrounds the opening. The reflective coating may be applied directly to a surface of the optics carrier by a surface coating method. With this embodiment of the beam splitting optics, it is possible to omit a clamping element which is necessary for securing the polarization beam splitter. Since the surface to which the reflective coating is applied is integrated into the optics carrier, this ensures that the beam splitting optics and the optics carrier will change uniformly under the influence of temperature, and tilting of the beam splitting optics will be prevented. The stability of the measuring device is increased and the mounting and adjustment effort required for the beam splitting optics are reduced at the same time. A reduction in the mounting and adjustment effort leads to a reduction in the manufacturing cost of the measuring device.
An aperture integrated into the optics carrier is preferably arranged between the beam source and the beam splitting optics in the beam path of the laser beam. The beam splitting optics is embodied, for example, as a polarization beam splitter, as a pinhole mirror or as some other suitable beam splitting optics. The aperture serves to limit the beam angle and/or the numeric aperture of the beam source and to adjust the geometry of the laser beam to the beam splitting optics and the beam forming optics. As an alternative or in addition to the aperture, a light trap is preferably arranged between the beam source and the beam splitting optics, integrated into the optics carrier. The light trap serves to absorb any light of the beam source striking it and also prevents unwanted reflection. Optical and electrical crosstalk from the beam source to the detector is reduced by the aperture and/or the light trap. The adjustment effort is reduced because the aperture and/or the light trap is/are integrated into the optics carrier. The adjustment of the aperture and the light trap relative to the beam source is already performed at the time of manufacturing the receptacles for the optical components in the optics carrier.
In a preferred embodiment, the optics carrier is made of a metallic material. Metallic optics carriers result in electrical shielding between the electro-optical components and reduce the electrical crosstalk between a beam source and a detector.
In a preferred embodiment, the optics carrier is embodied as a die-cast part. The embodiment as a die-cast part has the advantage that complex geometries can be created with a high precision. Die-cast parts have smooth clean surfaces and edges. Furthermore, die casting methods, especially using zinc, allow the production of smaller wall thicknesses in comparison with manufacturing methods such as injection molding or die casting with other metals, e.g., aluminum. Since the optics carrier is manufactured as a die-cast part, complex functions such as spring elements or boreholes can be integrated into the optics carrier without any complex post-processing. This reduces the cost of manufacturing the optics carrier and makes it possible to design an inexpensive measuring device.
The optics carrier is especially preferably designed as a die-cast part made of zinc or zinc alloys which are summarized under the term “zinc”. Zinc can be processed with a high precision in die-casting methods and also have a high thermal stability so that fluctuations in temperature, to which laser distance measuring system are often exposed, have only a minor influence on the adjustment status and thus on the measurement properties of the laser distance measuring systems. Various surface coatings are possible with zinc, so that reflective or absorbent coatings can be applied directly to the optics carrier. Zinc also has good electrical shielding properties.
Exemplary embodiments of the invention are described below on the basis of the drawings. These drawings do not necessarily show the exemplary embodiments drawn to scale but instead the drawings are embodied in schematic and/or slightly distorted form, where this serves the purpose of illustration. With regard to the addition of teachings that are discernible directly from the drawings, reference is made to the relevant state of the art. It should be pointed out here that various modifications and changes can be made with regard to the form and the detail of an embodiment without going beyond the general scope of the invention. The features of the invention disclosed in the description, the drawings and the claims, either individually or in any combination, may be essential for this refinement of the invention. Furthermore, all combinations of at least two of the features disclosed in the description, the drawings and/or the claims fall within the scope of the invention. The general idea of the invention is not limited to the precise form or the detail of the preferred embodiment described and illustrated below nor is it limited to a subject which would be restricted in comparison with the subject claimed in the claims. With given dimension ranges, values within the specified limits should also be disclosed as limit values and can be used and claimed as desired. For the sake of simplicity, the same reference numerals are used below for identical or similar parts or parts having an identical or similar function.